Uneven erosion in piping systems, especially elbow fittings, leads to pipe failure or early fitting replacement, either of which is costly in material, manpower and downtime. Applications for transporting and pumping fluids and media comprising abrasive contents, such as coal and sand slurries, wet sand, gravel and similar contents, suffer especially high costs from uneven component wear.
When fluids/media pass through an elbow fitting, the change in direction creates turbulent conditions, flow separation and vortex shedding along the pipe wall at the inside of the bend, and may create standing eddies causing backflow conditions at points along the fitting pipe walls. The conditions generally cause the elbow fitting pipe wall along the outside of the bend to erode substantially faster than the pipe wall along the inside of the bend, as the fluid/media impinges directly against the wall along the outside of the bend as it enters the fitting and changes direction. Additionally, heavier solids and particulates will be thrown to the outside wall as the fluid/media changes direction, so will continually scour the outer wall with new solid/particulate materials. In addition to high rates of localized wear on pipe walls, the turbulence and flow separation in the elbow fittings create head loss which must be compensated for by higher pressure pumps, and can create severe vibration and heating problems in the piping system.
Long radius elbow fittings and pipe sections can reduce these effects. However, long radius fittings require a great deal of space relative to standard short radius fittings. Additionally, long radius fittings still suffer accelerated erosion rates along the pipe wall along the outside of the bend because momentum still causes heavier particulate materials to be thrown to the outer wall, and they are continually scoured by new particulate/aggregate material.
A similar uneven erosion effect is experienced in long straight pipe runs, as the concentration of particulates will increase in the lower region of the fluid in long straight runs, making the bottom portion of the fluid stream more abrasive the upper portion. Additionally, in large diameter piping systems, the weight of the fluid and media is born by the lower pipe wall portion, causing higher erosion rates.
The inventors developed a new elbow fitting design which substantially eliminates uneven erosion within the fitting by inserting helix vanes along the outside pipe wall, which rotates the fluid around the piping centerline axis through the bend of the fitting. In addition, the elbow cross section is expanded in the direction of the outside pipe wall, which traps a layer of particulates in the helix channels between the helix vanes. During steady flow conditions, the fluid/media stream continuously erodes and redeposits this deposit layer rather than directly against the pipe wall. The rotation causes the fluid/media stream to follow nearly equal path lengths through the elbow fitting, and forces flow along the inside pipe wall as well as the outside pipe wall, with a more uniform velocity profile around the entire pipe wall, such that pipe wall erosion is distributed evenly around the circumference of the pipe wall throughout the elbow fitting. The beneficial even pipe wear has been found to extend far downstream of a helix elbow fitting as well.
The inventors discovered additional benefits, as well. Head loss through a helix elbow fitting was found to be substantially less than conventional elbow fittings. The inventors believe this is due to several factors. The helix vanes and channels channelize the flow closest to the pipe wall, thereby maintaining laminar flow conditions (or closer to laminar flow conditions) within the channels through the elbow fitting. The rotation causes all of the fluid streams to follow substantially equal path lengths through the fitting, reducing or eliminating flow separation and eddy losses. Additionally, rotating the fluid streams around the pipe wall circumference creates a longer effective bend radius as the flow streams follow longer paths through the same bend angle. Finally, the clockwise rotation creates a resulting torque vector, based on the Right Hand Rule, which aligns with the nominal pipe centerline, similar to a rifling effect.
The inventors found that the improved erosion profiles and head loss reduction extended far downstream, as well. The inventors therefore developed helix straight fittings for installation in straight piping runs as well. The rotation imparted on the fluid/media streams substantially eliminated localized bottom wall erosion downstream, and reduced head loss in the downstream piping runs. The expanded cross-section of the helix portion provided a similar sacrificial deposit layer, reducing erosion along the fitting pipe walls.
For general applications, the inventors found that at least three helix vanes were necessary to impart sufficient rotation on the fluid/media stream. However, the optimum number and spacing of the helix vanes is dependent on the anticipated fluid/media properties, including pressure, flow velocity, specific gravity, viscosity, temperature, particulate loading and size, incline, angle of change, and pipe material. Optimization can be performed using flow modeling software that is widely available, as well as interpolating empirical data from installed systems, which is within ordinary skill of persons in this field.
The inventors found that the downstream flow improvements from the helix straight fittings could be used to improve discharge hose performance as well, for example in firefighting situations, water blasting operations, irrigation applications, water cannons, and other applications requiring accurate projection of a concentrated fluid stream over a distance. Installing a helix discharge amplifier immediately upstream of a discharge nozzle created a very concentrated discharge stream, due to the rotation, with improved discharge velocity due to the reducing effect and reduced head loss through the discharge nozzle. Additionally, the improved concentration provided by the stream rotation eliminated the need for flow straighteners upstream of the discharge nozzles, eliminating a major source of head loss.
An additional, unanticipated benefit was obtained from the helix discharge amplifier. Newton's Third Law of Motion states that when one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body. The result, for firefighters operating firehoses, is that the hose operators must exert a force equal to the force of the water exiting the hose nozzle in order to control the hose nozzle—i.e. the force of over a hundred gallons per minute of pressurized water, referred to as “back pressure” or “hose kick”. Normally, three firefighters are required to operate a single 1.5-inch or 2.5-inch hose/nozzle due to the reaction force, referred to as “hose kick” or “kickback”. The nozzleman holds and directs the discharge nozzle itself. The backup nozzleman physically supports the nozzleman, assists in holding up the weight of the hose and nozzle, and provides relief when the nozzleman becomes fatigued. The hoseman assists in moving the hose behind the nozzleman and backup nozzleman, to align it with the nozzle orientation so the nozzle is easier to direct, and provides relief when the others become fatigued. However, installing a helix discharge amplifier immediately upstream of the nozzle virtually eliminated hose kick. In testing, the improvement was so substantial that a single firefighter could operate the hose nozzle for extended periods, without backup, and even hold and direct the nozzle with one arm. The discharge stream was also much more focused and accurate, and maintained this concentration and accuracy over a longer distance.